A boost pressure control system is known, for example, from German Patent No. 195 02 150. A valve in a bypass of the exhaust-driven turbocharger turbine serves as the actuator for the boost pressure. The manipulated variable for the bypass valve is generated by a PID controller which generates a proportional component, a differential component, and an integral component for the manipulated variable. It defines for the integral component a limit value which is derived from operating parameters of the internal combustion engine.
As a rule, a bypass valve for the exhaust-driven turbocharger turbine is used as the actuator. A device which changes the turbine geometry can also, however, be used as the actuator. With all these actuators, especially with a bypass valve that is controlled or regulated via a spring-loaded pressure capsule in conjunction with an electropneumatic timing valve, there exists a nonlinear correlation between the boost pressure generated by the turbocharger and the manipulated variable for the actuator. This nonlinear relationship may be ignored as long as the working point of the boost pressure controller shifts only within very narrow limits. In this case the boost pressure as a function of the manipulated variable can be regarded as almost linear. If, however, the working range of the boost pressure controller should not be confined only to a very narrow working range, but rather if a wide working range, i.e. a large variation range for the manipulated variable, is required, then with a greater displacement of the working point on the one hand the control action becomes too slow, and on the other hand overshoots occur in the control system. If the same turbocharger components are to be used in engines with different outputs, it is mandatory that the boost pressure controller be designed for a wide working range.
It is therefore an object of the present invention to provide a method with which the boost pressure controller can be operated over the widest possible working range without resulting in any slowing of the control action or overshoots in the control system.